Category Archives: Mechanical methods

Even the coolest criminal cannot hide a guilty countenance. Susan Gaidos tests her mettle against a new breed of lie detector

It is hard not to feel a little nervous. Andrew Ryan is trained to catch liars, and I am sitting in his lab at the US Department of Defence Polygraph Institute, preparing to lay a bald-faced whopper on him. Earlier today, I participated in a mock crime, a short-lived melee that ended in aggravated assault, attempted murder and robbery. The act of stabbing a dummy in the chest and rifling through its purse has left me feeling more than a little guilty. My accomplice has instructed me to reveal nothing. But will my discomfort give me away?

The authors examined the incremental validity of the reaction time (RT) measure beyond that of skin conductance response (SCR) in the detection of concealed information. Participants performed a Stroop-like task in which they named the color of critical and neutral words. Results show that the SCR highly differentiated between the relevant and neutral words. However, the RT demonstrated a significant differentiation only when the critical words denoted personally significant items (e.g., one’s own name) and not when they denoted crime-relevant items related to a simulated crime. In both cases, combining the 2 measures yielded no advantage over the use of SCR alone. Thus, although behavioral measures may differentiate between relevant and neutral information in some cases, their practical use is questionable. (PsycINFO Database Record (c) 2005 APA, all rights reserved)

When people lie, they use different parts of their brains than when they tell the truth, and these brain changes can be measured by functional magnetic resonance imaging (fMRI), according to a study presented today at the annual meeting of the Radiological Society of North America. The results suggest that fMRI may one day prove a more accurate lie detector than the polygraph.

“There may be unique areas in the brain involved in deception that can be measured with fMRI,” said lead author Scott H. Faro, M.D. “We were able to create consistent and robust brain activation related to a real-life deception process.”

[…] American researchers are exploring lie-detection technologies that may banish polygraph machines to the history books. At the University of Houston, a computer scientist is trying to uncover lies by measuring heat levels in the face. In South Carolina, a professor hopes she has found the key to deception in brain waves. Elsewhere, researchers are looking at everything from speech patterns to eye movements to “brain fingerprints.” Success remains elusive, however, and no newfangled lie-detection machines appear ready for prime time. Skeptics, meanwhile, doubt that any technology will improve much on the mixed record of polygraph machines, which are often used in the United States to screen employees and test the truthfulness of criminal suspects.

The polygraph is still the most popular tool for ferreting out the guilty. Strange, says David Lykken. Not only is it easy to beat, there is also no evidence that it works

HOW do you tell if someone is lying? Easy, according to many of those who should know the answer, such as US government law enforcement and intelligent agencies: hook them up to a polygraph lie detector. The FBI regularly uses the polygraph in national security investigations, and evidence from it is even admissible in some civilian courts in the US. Now the British government seems to share this optimism about the polygraph’s truth-divining capabilities: last week it revealed it is considering making it mandatory for testing sex offenders.

The trouble is, the polygraph doesn’t work – at least, not in any scientific sense. There is plenty of evidence for its inefficacy. A 2002 report by the US National Academy of Sciences even equated polygraph screening with voodooism. Worse, it can lead to serious miscarriages of justice.

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